1. Field of the Invention
The invention relates to a gas analyzer and method for measuring the concentration of a gas component in the gas analyzer.
2. Description of the Related Art
EP 1 475 618 B1 discloses a conventional method and gas analyzer.
The known gas analyzer is a laser spectrometer which, in particular, is used for optical gas analysis in process metrology. A wavelength-tunable light source comprising a laser diode generates light in the infrared range, which is guided through a process gas (sample gas) to be measured and subsequently detected. The wavelength of the light is tuned to a specific absorption line of the respective gas component to be measured, where the laser diode samples the absorption line periodically in a wavelength-dependent manner. To this end, the laser diode is actuated by a ramp-shaped or triangular current signal within periodically successive sampling intervals. During the comparatively slow sampling of the absorption line, the wavelength of the generated light is additionally modulated sinusoidally with a high frequency and small amplitude. The profile of the absorption line is nonlinear. As a result, harmonics above the modulation frequency are also generated in the measurement signal obtained during the detection. The measurement signal is usually demodulated at an n-th overtone, preferably the second harmonic, using a phase-sensitive lock-in technology and evaluated to form a measurement result for each sampling interval. In the case of a small modulation amplitude, the detection of the n-th harmonic is directly proportional to the n-th derivative of the direct measurement signal. By way of example, the evaluation is brought about by fitting (i.e., curve fitting) the profile of the demodulated measurement signal (i.e., intended curve), to be expected in the ideal case, to the actual profile (i.e., actual curve) thereof. Finally, the concentration of the gas component to be measured is determined from the measurement result obtained in the process.
The detection and determination limit for measuring the concentration of the gas component are restricted by the noise of the gas analyzer (e.g., laser noise, and/or detector noise), which is superposed on the measurement signal.